Film-thickness and composition dependence of epitaxial thin-film PZT-based mass-sensors

• We examine the epitaxial PZT thin films with various thicknesses and compositions.
• Cantilevers consist of all-oxide piezoelectric stacks and silicon devices.
• Reduction in interfacial and clamping effects with increasing film thickness.
• Transverse piezoelectric coefficient and mass-sensitivity peak on the tetragonal side.
• Epitaxial PZT thin film enhances the mass-sensitivity.

The transverse piezoelectric coefficient e31,f and mass-sensitivity were measured on piezoelectric cantilevers based on epitaxial PZT thin-films with film-thicknesses ranging from 100 to 2000 nm. The highest values of e31,f and mass-sensitivity were observed at a film thickness of 500–750 nm, while the observed remnant polarization Pr and longitudinal piezoelectric coefficient d33,f values become saturated with a film thickness of 750–1000 nm. To obtain high performance by making use of its optimal film thickness, PZT thin films with various Zr/Ti ratios from 20/80 to 80/20 were studied. The experimental results indicated that the ferroelectric property reached a highest remnant polarization Pr at a Zr/Ti ratio of 20/80, while the longitudinal piezoelectric coefficient d33,f increased with increasing Zr content and reaches a maximum at a Zr/Ti ratio of 52/48. The findings suggest that the optimal composition for mass-sensitivity and transverse piezoelectric coefficient e31,f was shifted to the tetragonal part of the phase diagram with the Zr/Ti ratios of 45/55 and 40/60, respectively.